I emailed their CEO earlier today and received a response back from one of their senior software engineers
“Patrick forwarded your Email concerning LPCM down-mix issues and I can give you an update on that. The engineering team is currently working on the issue as we speak. There are two steps here, one is to correct the downmixing in the case where there are no discrete surrounds and the other is when there are discrete surrounds. We have completed the first step and we are testing the fix and now working on the second step.
At this time I am unable to give you an exact date for availability of the SW fix but know that we are addressing it and when I know more, I will let you know.”
Hopefully it’s not that far away
Wow, this is taking a long time to fix. You would think this is trivial since downmixing is something that has been around for a long time. Should be not really a problem for a company that has, I suspect, lots of audio experts. Don’t get me wrong. I’m heavily invested in Sonos, and I have no other choice than to wait. I’m just really surprised this was even missed in the first placed when launching the Arc.
Wow, this is taking a long time to fix. You would think this is trivial since downmixing is something that has been around for a long time. Should be not really a problem for a company that has, I suspect, lots of audio experts. Don’t get me wrong. I’m heavily invested in Sonos, and I have no other choice than to wait. I’m just really surprised this was even missed in the first placed when launching the Arc.
I couldn’t have said it better myself. And I believe it was said that a fix would be anticipated this past July. A shame. I love my speakers; but I expect better.
LG CX and PS5 with Sonos Arc here. I’m using the settings below and getting some pretty solid sound with Dolby Multichannel PCM 5.1. So far any other setting results in Stereo PCM 2.0 and sounds worse. I know it’s not LPCM, but so far I can’t get anything else to work.
LG CX:
HDMI Input Audio Format: Bitstream
Digital Sound Out: Auto
PS5:
Audio Format (Priority): Bitstream (Dolby)
HDMI Device Type: AV Ampoifier
Number of Channels: 5.1ch
The thing is Sonos clearly needs to fix a few bugs here. First of all there is no such thing as Dolby Multichannel PCM 5.1, so they need to work out why the Sonos Arc reports it as this.
It’s also clear that there is some kind of handshaking issue between LG TV’s and the Sonos Arc where it’s telling the TV it can process LPCM 7.1 but then not downmixing it properly to 5.1.
Hi All.
As mentioned previously, this is an issue we’re aware of.
Currently, Sonos does support multichannel LPCM in 5.1 mode on the Arc, but does not support multichannel LPCM in 7.1 mode - Downmixing LPCM 7.1 to 5.1 is a feature we are currently working on, however; we do not have any further information to share with you at this time. Rest assured, we will address this in a forthcoming update.
Add my name to the plate, I’m really excited about a proper downmix from LPCM 7.1 to LPCM 5.1. I’m not angry or anything, but man…my 4K library is only half loved right now. This would certainly get me on board for some new speakers for other purposes :)
Another new Arc owner here with a 5.1 setup, and an LGC1 having this issue.
I’m kind of amazed scrolling back how long this has gone on without a fix. Somewhat disheartening.
Right? I really hope they won't let it die… it's a significant issue for many people…
I hoped they fixed it with the recent update but they didn't :(
So, it looks like this might be the reason: https://en.community.sonos.com/home-theater-228993/lpcm-eta-for-arc-6842558?postid=16488286#post16488286
TL:DR, it looks like LPCM 7.1 is downmixed incorrectly with side channels coming out the rear and rear channels not coming out at all. Back to Dolby Bitstream it is. (And back to having to switch modes between Atmos and non-Atmos on Apple TV 4k too.) Sigh.
I know Sonos doesn’t do ETAs, but can we at least get an official acknowledgement of this problem?
Yeah, something is definitely wrong with the channels on Multichannel PCM. Sound coming out the wrong channels or not at all.
Hi @ledzep1
This has not yet been addressed. I too have seen mention that it seems to have improved - I don’t see why this would be the case (wishful thinking?).
As it counts as a new feature, rather than a bug fix, I would suggest that it will be specifically mentioned in the release notes, when it does arrive.
Another new Arc owner here with a 5.1 setup, and an LGC1 having this issue.
I’m kind of amazed scrolling back how long this has gone on without a fix. Somewhat disheartening.
I am sure this has already been mentioned, but the Apple TV is also receiving the same issue with the audio being interpreted as Multichannel 7.1; just like my PS5. I did not have this issue with my Chromecast w/ Google TV.
You would think after the CEO tweeted about a fix being in the works during this past summer, that it would be here now. I have no idea what Sonos is doing.
Perhaps its not an issue as such, and just how the lg and sonos arc report everything in LPCM as 7.1.
I must admit when the sonos arc reports something as multichannel pcm 7.1 it sounds fine to me.
i don’t have any rears though, just the ARC and Sub here.
In any case It would be nice if someone from support could respond, as much as I love sonos, I think their communication could be a lot better.
Perhaps its not an issue as such, and just how the lg and sonos arc report everything in LPCM as 7.1.
I must admit when the sonos arc reports something as multichannel pcm 7.1 it sounds fine to me.
i don’t have any rears though, just the ARC and Sub here.
In any case It would be nice if someone from support could respond, as much as I love sonos, I think their communication could be a lot better.
Well, Sonos already admitted it’s an issue. It is very noticeable when you have rear speakers. Just hope it doesn’t take as long as adding DTS support to fix this *wink*
I am having this same issue on the PS5. I tried selecting the PS5 option of connecting to an AV receiver and using a 5.1 setup but I am still missing audio channels. Anyone know what the exact issue is?
For those having issues with the LG CX outputting MultiChannel 7.1 to the Sonos ARC, have you tried changing the sound output to Auto instead of passthrough? This fixed the issue and changed it to Multichannel 5.1 for me.
Changing it to Auto changes the output to Dolby Multi-channel PCM 5.1, which is not the same as Multichannel PCM (LPCM) as far as I know.
It shows in the Sonos App as Multichannel PCM 5.1 when playing Dolby 5.1 content and shows as Dolby Atmos when playing Atmos content (Not DD+ Atmos). From my understanding this is what you would expect to see, since Sonos doesn’t do 7.1.
For those having issues with the LG CX outputting MultiChannel 7.1 to the Sonos ARC, have you tried changing the sound output to Auto instead of passthrough? This fixed the issue and changed it to Multichannel 5.1 for me.
Changing it to Auto changes the output to Dolby Multi-channel PCM 5.1, which is not the same as Multichannel PCM (LPCM) as far as I know.
It shows in the Sonos App as Multichannel PCM 5.1 when playing Dolby 5.1 content and shows as Dolby Atmos when playing Atmos content (Not DD+ Atmos). From my understanding this is what you would expect to see, since Sonos doesn’t do 7.1.
Ok that is nice, unfortunately not in my case. I’m using an Apple TV 4K and not a PS4 so perhaps there is a difference there. Have to do some more experimenting.
I’m using an Apple TV 4K as well at the moment on an LG CX and getting these results. I’ve left the Apple TV on Auto, Atmos Available for Audio and I have set HDMI Input Audio on the TV to Bitstream and Audio Output to Auto. It’s really weird how so many of us are getting different results.
can you make the PS4 output lpcm 5.?
Unfortunately not. The only options on the PS4 Pro are Linear PCM, Bitstream (Dolby), and Bitstream (DTS). It’s cool you can choose 5.1 or 7.1 on the Switch, and cool that there’s a PS5 option to make it send the right thing too.
For the AppleTV, changing the CX to output Auto instead of Passthrough sends “Dolby Multichannel PCM 5.1”, which is subtly different from “Multichannel PCM 5.1”, in that it’s somewhat compressed. I don’t know that I would personally be able to tell the difference between those, but as others have said, if you want uncompressed best-quality sound from Blurays, you need the CX to use Passthrough.
Regardless, Sonos will tell you if it’s receiving a signal it can’t process, like DTS. Seeing as it’s receiving a Multichannel 7.1 signal, and not telling me it can’t process it, I would consider sending sound out of the wrong speakers a bug 
Is this issue only with the LG CX?
Anything in DD 5.1 on apple4k tv is output as multichannel pcm 7.1
Blurays on my oppo203 in 5.1 output as 7.1
setting series x to uncompressed 5.1 outputs as multichannel pcm 7.1
Unsure if this topic relates to the same issue, can someone from Sonos please confirm, I have had this issue since the LPCM update you released, and it would be nice to know if it is indeed an issue with the Sonos?
Thank you
It's not your TV, the Arc needs a software update to handle downmixing properly
Is this issue only with the LG CX?
Anything in DD 5.1 on apple4k tv is output as multichannel pcm 7.1
Blurays on my oppo203 in 5.1 output as 7.1
setting series x to uncompressed 5.1 outputs as multichannel pcm 7.1
Unsure if this topic relates to the same issue, can someone from Sonos please confirm, I have had this issue since the LPCM update you released, and it would be nice to know if it is indeed an issue with the Sonos?
Thank you
Yes it is only with the LG BX/CX/GX from what I can tell.
My Sony A8H with eARC passes 5.1 PCM without any issues from the Apple TV, Nintendo Switch etc. My LG CX always had the 7.1 PCM issue.
Add it to the list of issues with the LG CX. Thankfully, generally LG end up patching their issues eventually even though they often break other things in the process.
For me, I’d rather not deal with the level of incompetence LG brings to such expensive products. They’ve always had issues with Sonos equipment in terms of dropouts, lip sync etc.
Did the latest system update version 13.0 fix this issue , has anyone tried it yet?
I believe it’s helped with dropouts for some tv owners, I will be pretty disappointed to finally get an update system side and doesn’t fix this as well.
Doesn’t fix this issue
Shame, perhaps now we have version 13, minor fixes will come along soon.
It’s really just a software issue, so I see no reason for 7.1 downmixing support not to arrive on the Arc. As for how long it will take, I don’t have that information.
Generally, Sonos will not say anything about a feature until it’s already ready. As we’re already confirming we’re working on this, we’re committed and the Arc will downmix 7.1 LPCM at some point. The official line is “This is a feature we are currently working on, however; we do not have any further information to share with you at this time. Rest assured, we will address this in a forthcoming update.”
So, you should be good to keep your Arc beyond the return period.
Thank you for your reply. Just placed an order for an Arc 
I emailed their CEO earlier today and received a response back from one of their senior software engineers
“Patrick forwarded your Email concerning LPCM down-mix issues and I can give you an update on that. The engineering team is currently working on the issue as we speak. There are two steps here, one is to correct the downmixing in the case where there are no discrete surrounds and the other is when there are discrete surrounds. We have completed the first step and we are testing the fix and now working on the second step.
At this time I am unable to give you an exact date for availability of the SW fix but know that we are addressing it and when I know more, I will let you know.”
Hopefully it’s not that far away
UPDATE: (not a good one sadly)
My apologies for not replying, things are hectic here and it fell through the cracks.
The fix is still undergoing testing. Due to the way we handle SW releases, we are expecting these fixes to turn up in our July SW update.
Hi @billiejoe87
I really strongly believe that Sonos is unintentionally misleading us with their supposed fix for this issue.
Sonos will add downconversion for LPCM 7.1 to LPCM 5.1, however I think the issue with LG TV’s incorrectly sending all LPCM audio as LPCM 7.1 won’t be fixed as it’s an LG problem. The LG’s wrongly send all LPCM as LPCM 7.1 even if it’s only LPCM 5.1 audio.
I really hope I’m wrong, but I feel Sonos announcement that the issue was on their own end has made everyone not put pressure on LG to fix their own issue with incorrectly sending the wrong audio. As someone else here said, if you use a HDFury device or a Sony TV the issue goes away.
To be clear, I was addressing the original post, in which PCM was being selected as the output format on the source device.
If your LG TV is converting another format to 7.1 LPCM without being told to, then that is indeed an issue with the TV.
Is it really asking much for Sonos to contact LG and make them aware of the issue for all LG owners that own the Sonos Arc?
No, but it would not count as much as numerous LG TV owners getting in touch and doing the same. If we were to inform them (and perhaps we have already), but there wasn’t a significant volume of LG customers getting in touch with LG about the same issue, they wouldn’t take it as a priority. Customer contact volume is the only thing that will drive them assign the problem with a higher priority. I therefore recommend that you do get in touch with LG.
